Optical forces allow manipulation of small particles and control of nanophotonic structures
with light beams. While some techniques rely on structured light to move particles using field intensity gradients, acting locally, ...[+]

Optical forces allow manipulation of small particles and control of nanophotonic structures
with light beams. While some techniques rely on structured light to move particles using field intensity gradients, acting locally, other optical forces can push particles on a wide area of
illumination but only in the direction of light propagation. Here we show that spin orbit
coupling, when the spin of the incident circularly polarized light is converted into lateral
electromagnetic momentum, leads to a lateral optical force acting on particles placed above a substrate, associated with a recoil mechanical force. This counterintuitive force acts in a direction in which the illumination has neither a field gradient nor propagation. The force direction is switchable with the polarization of uniform, plane wave illumination, and its magnitude is comparable to other optical forces.[-]